Refrigerant system with bypass line and dedicated economized flow compression chamber

ABSTRACT

A refrigerant system has an economizer cycle. A vapor refrigerant from the economizer loop is returned to a dedicated economizer compression chamber. A main refrigerant is returned to a dedicated main compressor chamber. A bypass line communicates the two refrigerant flows.

BACKGROUND OF THE INVENTION

This application relates to a refrigerant system having an economizercycle, and wherein an economized refrigerant flow is returned to aneconomizer compression chamber of a compression unit, and a mainrefrigerant flow is returned to a main compression chamber of acompression unit, wherein a bypass refrigerant line communicates the tworefrigerant flows upstream of their corresponding compression chambers.

Refrigerant compressors compress and circulate a refrigerant throughouta refrigerant system to condition a secondary fluid, typically deliveredto a climate-controlled space. In a basic refrigerant system, acompressor compresses a refrigerant and delivers it to a heat rejectionheat exchanger. Refrigerant from the heat rejection heat exchangerpasses through an expansion device, in which its pressure andtemperature are reduced. Downstream of the expansion device, therefrigerant passes through a heat accepting heat exchanger, and thenback to the compressor. As known, the heat accepting heat exchanger istypically an evaporator, and the heat rejecting heat exchanger is acondenser for subcritical applications and a gas cooler fortranscritical applications.

One option in a refrigerant system design to enhance performance is theuse of an economizer, or vapor injection function. When an economizerfunction is activated, a portion of refrigerant is tapped from a mainrefrigerant stream downstream of the heat rejection heat exchanger. Inone configuration, this tapped refrigerant is passed through anauxiliary expansion device, to be expanded to an intermediate pressureand temperature, and then this partially expanded tapped refrigerantpasses in heat exchange relationship with a main refrigerant flow in aneconomizer heat exchanger. In this manner, the main refrigerant flow iscooled such that it will have a greater thermodynamic potential when itreaches the heat accepting heat exchanger. The tapped refrigerant,typically in a superheated thermodynamic state, is returned to thecompressor.

As known, an economizer function can be performed in either a flash tankor in an economizer heat exchanger. For purposes of this application,the two devices will be both known as an “economizer heat exchanger.”

As described in European Patent Application EP1498667, the vaporrefrigerant is returned to a dedicated economizer compression chamber ora compressor. The main refrigerant flow is returned from the heataccepting heat exchanger back to its own dedicated compression chamberor compressor. This known system maintains the economizer and suctionrefrigerant flows completely isolated from each other. A purpose of thededicated compression chambers is to have two separate non-mixing inletrefrigerant streams, each compressing refrigerant from a particularthermodynamic state to a common discharge thermodynamic state.

SUMMARY OF THE INVENTION

In a disclosed embodiment of this invention, a refrigerant system isprovided with an economizer cycle, where an economized refrigerantstream is returned from the economizer circuit back to a dedicatedeconomizer compression chamber (or a separate compressor) through aneconomizer circuit return line. A main refrigerant stream is returned toits own dedicated main compression chamber (or a compressor) through asuction line. A bypass line communicates the two refrigerant flow linesupstream of their corresponding inlets to the dedicated compressionchambers (or compressors). In this arrangement, the two inletrefrigerant streams are allowed to selectively communicate and mix witheach other via the bypass line. In one embodiment, the bypass line mayhave a small orifice which always communicates the two refrigerantstreams. In a second embodiment, the bypass line may include acontrolled valve. In a third embodiment, the bypass line may include acombination of these two options.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art system.

FIG. 2 shows a schematic of a first embodiment.

FIG. 3 shows a schematic of a second embodiment.

FIG. 4 shows a schematic of a third embodiment.

FIG. 5 shows a schematic of a fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a prior art refrigerant system 20. As known a compressionunit 22 includes at least two chambers, cylinders, or compressors 24 and26. The two compression chambers compress refrigerant and deliver itdownstream to a heat rejection exchanger 28. The heat rejectionexchanger 28 can be a condenser (if the refrigerant dischargethermodynamic state is below the critical point) or a gas cooler (if therefrigerant discharge thermodynamic state is above the critical point).An expansion device 29 is positioned downstream of the heat rejectionheat exchanger, and partially expands refrigerant passing into a flashtank 30 to an intermediate pressure. An expansion device 34 ispositioned downstream of the flash tank 30, to control the amount ofrefrigerant reaching an evaporator 36, and expands this refrigerant to apressure approximating the suction pressure. In the flash tank 30, aliquid refrigerant is separated from a vapor refrigerant. The liquidrefrigerant from the flash tank 30 is expanded to a two-phasethermodynamic state in the expansion device 34, flows through theevaporator 36, where it evaporates and is typically superheated, passesthrough a suction line 38 and is returned to the dedicated maincompression chamber 26. The separated vapor refrigerant passes through areturn line 32 of the economizer circuit to its dedicated compressionchamber 24. In the known prior art system, the lines 32 and 38 aremaintained strictly separate. A purpose of the two separate linesdelivering refrigerant to two dedicated compression chambers 24 and 26is to have refrigerant in each of the compression chambers be closer tohomogeneous conditions than if the two refrigerant flows were allowed tomix.

FIG. 2 shows an embodiment 40 wherein the compression unit 42 has adedicated economizer compression chamber 44 and a dedicated maincompression chamber 46. However, a bypass line 48 including arestriction 49 is provided to communicate an economizer refrigerant flowand a main refrigerant flow. This restriction can be in a form of anorifice; however it can also be a capillary tube or any other type of arestriction that throttles the refrigerant flow. Typically the size ofthe orifice is selected to have a cross-sectional area between 0.1 to 3square millimeters. Other restriction types may have a differentcross-sectional area; however their effective cross-sectional area issized to correspond to an equivalent orifice area in the range mentionedabove.

A purpose of this bypass line 48 is to allow pressure equalization onstartup. This will allow reduce motor starting torque, resulting in amore efficient operation, and allow the use of smaller and lessexpensive motors. Also, the orifice allows drainage of lubricating oilfrom the economizer line 32 to the suction line 38 after shutdown. Ashutoff valve 33 may be included on the economizer circuit return line32.

FIG. 3 shows an embodiment 50 having a compression unit 52 havingdedicated compression chambers 54 and 56. The bypass line 58 includes anelectrically controlled valve, which in this embodiment is disclosed asa controlled solenoid valve 59, which may be opened or closed. Thesolenoid valve may be opened to allow mixing of main and economizedrefrigerant streams during continuous operation, or can be opened priorto startup for pressure equalization, or can be opened at or aftershutdown for oil return. Also, in some circumstances, the valve 59 maybe operated in a pulse mode such as, for instance, to facilitate oilreturn or unload the compression unit 50. Further, the valve 59 may beof a modulating type to tailor valve opening to specific operatingconditions (operating pressures, in particular) and precisely matchthermal load demands in the conditioned space.

As shown in FIG. 4, a refrigerant system 60 has a compression unit 62with dedicated compression chambers 64 and 66, as in the priorembodiments. However, the bypass function now has both the solenoidvalve 59 on the bypass line 58 and an orifice 68 on a branch bypass line66. The embodiment 60 would achieve the benefits of each of theembodiments of FIGS. 2 and 3, and allow the control at shutdown orstartup without the need to open the valve 59. The bypass lines 58 and66 may be arranged in a parallel configuration, between the economizercircuit return line 32 and the main circuit suction line 38, as well.

FIG. 5 shows yet another embodiment 80 having a compression unit 82 withseparate compression chambers 84 and 86. In the embodiment 80, theeconomizer function is provided by an economizer heat exchanger 94,rather than the flash tank 30 of previous embodiments. As known, a tapline 90 taps a portion of refrigerant from a main refrigerant flowingthrough a liquid line 88 and passes this refrigerant through aneconomizer expansion device 92, where it is expanded to a lowerintermediate pressure and temperature. This would allow the refrigerantin the tap line 90 to further cool the main refrigerant in the liquidline 88, while passing through the economizer heat exchanger 94. Theeconomized refrigerant, typically in the vapor thermodynamic state,flows into the return line 96 of the economizer circuit. A main circuitexpansion device 34 is positioned downstream of the economizer heatexchanger 94 to control the amount of liquid refrigerant reaching theevaporator 36. While the economized refrigerant flow in the tap line 90and the main refrigerant flow in the liquid line 88 are shown passingthrough the economizer heat exchanger 94 in the same direction, inpractice, they are preferably flown in counterflow relationship. The tworefrigerant streams are shown flowing in the same direction forillustration simplicity only. Furthermore, the tap line 90 may bepositioned downstream of the economizer heat exchanger 94.

Similar to previous embodiments, the bypass line 58 is shown with thesolenoid valve 59. Further, the economizer heat exchanger 94 may beutilized in the embodiments of FIG. 2 or 4 as well, instead of the flashtank 30.

As stated above, the flow control device 59 may have an adjustableorifice to control the amount of communicated refrigerant between thededicated economizer and main compression chambers, based, for instance,on operating conditions and thermal load demand in the conditionedspace. On the other hand, the solenoid valve 59 may be controlled by apulse width modulation technique to achieve similar results forcompressor unit unloading or to facilitate oil return and assurereliable compressor operation.

It should be pointed out that many different compressor types could beused in this invention. For example, scroll, screw, rotary, orreciprocating compressors can be employed. The economized flow and mainflow chambers can be separate compressors, or these compression chamberscan be positioned within a single compressor. In the context of thisinvention, each compression chamber can be represented by a singlecylinder or multiple cylinders, as for example, may be the case for areciprocating compressor. If the compression chambers are located withina single compressor, then the bypass line can be located internally orexternally, in relation to the compressor shell. If the compressionchambers are independent compressors then the preferable location forthe bypass line would be external to these compressors. Further, each ofthe dedicated compression chambers may have a number of sequentialcompression stages, with the dedicated main compression chambers havinga higher number of sequential compression stages then the dedicatedeconomizer compression chambers, since they operate between higherpressure differentials.

This invention would apply to a broad range of refrigerants including,but not limited to, R744, R22, R134a, R410A, R407C, R290, R600a andtheir combinations.

The refrigerant systems that utilize this invention can be used in manydifferent applications, including, but not limited to, air conditioningsystems, heat pump systems, marine container units, refrigerationtruck-trailer units, and supermarket refrigeration systems. Therefrigerant system of this invention can be a subcritical oftranscritical system.

Although an embodiment of this invention has been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

1. A refrigerant system comprising: at least two compression chambers,said at least two compression chambers for compressing a refrigerant, adownstream heat rejection heat exchanger, a refrigerant line passingfrom the heat rejection heat exchanger into an economizer cycle, and amain refrigerant line passing from the economizer cycle through a mainexpansion device and to a heat accepting heat exchanger, a suction linedownstream of said heat accepting heat exchanger and extending to atleast one of the at least two compression chambers; a return line beingreturned from the economizer cycle to at least one other of the at leasttwo compression chambers; and a bypass line communicating the returnline and the suction line.
 2. The refrigerant system as set forth inclaim 1, wherein said bypass line includes a restriction to allowcontinuous communication between the return line and the suction line.3. The refrigerant system as set forth in claim 2, wherein said bypassline includes an electrically controlled valve to provide selectivecommunication.
 4. The refrigerant system as set forth in claim 3,wherein said electrically controlled valve is a solenoid on/off valve.5. The refrigerant system as set forth in claim 3, wherein saidelectrically controlled valve is controlled by a pulse width modulationtechnique.
 6. The refrigerant system as set forth in claim 3, whereinsaid electrically controlled valve is a modulating valve.
 7. Therefrigerant system as set forth in claim 3, wherein said electricallycontrolled valve is opened to equalize pressure upon refrigerant systemshutdown or before startup.
 8. The refrigerant system as set forth inclaim 2, wherein said restriction is an orifice.
 9. The refrigerantsystem as set forth in claim 2, wherein said restriction has across-section area between 0.1 square millimeter and 3 squaremillimeters.
 10. The refrigerant system as set forth in claim 2, whereinsaid restriction is a capillary tube.
 11. The refrigerant system as setforth in claim 1, further comprising an electrically controlled valveinstalled in parallel with said bypass line.
 12. The refrigerant systemas set forth in claim 1, wherein said economizer cycle includes a flashtank to separate liquid and vapor refrigerant phases.
 13. Therefrigerant system as set forth in claim 1, wherein said compressionchambers are independent compressors.
 14. The refrigerant system as setforth in claim 1, wherein said compression chambers are positionedwithin a single compressor.
 15. The refrigerant system as set forth inclaim 14, wherein said bypass line is located externally in relation tothe compressor.
 16. The refrigerant system as set forth in claim 14,wherein said bypass line is located internally in relation to thecompressor.
 17. The refrigerant system as set forth in claim 14, whereinsaid compressor is reciprocating compressor and said compressionchambers are reciprocating compressor cylinders.
 18. The refrigerantsystem as set forth in claim 1, wherein at least one of said at leasttwo compression chambers is represented by sequential compressionstages.
 19. The refrigerant system as set forth in claim 1, wherein saideconomizer cycle includes an economizer heat exchanger having aneconomizer expansion device expanding a tapped portion of refrigerantand passing it through the economizer heat exchanger to exchange heatwith the main refrigerant, with said tapped refrigerant being returnedthrough the return line.
 20. The refrigerant system as set forth inclaim 1, wherein at least one said compression chamber is a part of atleast one reciprocating compressor cylinder.
 21. The refrigerant systemas set forth in claim 1, wherein the refrigerant streams in said returnline and suction line are partially combined together at subcriticalpressure.
 22. The refrigerant system as set forth in claim 1, whereinsaid refrigerant is selected from a group consisting of R744, R22,R410A, R134a, R407C, R290, R600a refrigerants or their combinations. 23.A method of operating a refrigerant system comprising: providing atleast two compression chambers, said at least two compression chamberscompressing refrigerant and delivering the refrigerant to a downstreamheat rejection heat exchanger, refrigerant passing from the heatrejection heat exchanger into an economizer cycle, and a main flow ofrefrigerant passing from the economizer cycle through a main expansiondevice and to a heat accepting heat exchanger, refrigerant from the heataccepting heat exchanger passing through a suction line to at least oneof the at least two compression chambers; an economized flow ofrefrigerant, that is at least largely vapor, being returned from theeconomizer cycle to at least one other of the at least two compressionchambers through a return line; and communicating the return line andthe suction line through a bypass line.
 24. The method as set forth inclaim 23, wherein an electrically controlled valve on said bypass lineis opened to unload the refrigerant system.
 25. The method as set forthin claim 23, wherein an electrically controlled valve on said bypassline is opened to return oil.